Single shaft shifting mechanisms for selecting and engaging or disengaging the selectable ratios of a multiple-speed vehicular mechanical transmission are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,621,537; 4,920,815; 5,285,694 and 5,297,453, the disclosures of which are incorporated herein by reference. Such mechanisms provide alternative arrangements to the multiple parallel shift rail-type devices as disclosed in U.S. Pat. Nos. 4,445,393; 4,275,612; 4,584,895 and 4,722,237, the disclosures of which are incorporated herein by reference.
Both the multiple rail and single shaft shifting mechanisms typically provide a biasing mechanism to urge the gear selection lever to a position which may vary depending upon the particular shift pattern. For example, a biasing mechanism may be utilized to provide additional resistance when selecting the reverse or low (creeper) ratio so the driver does not inadvertently select these ratios. The biasing mechanism may also provide a force to move the shift lever laterally away from a particular rail selection when no driver force is applied. The prior art biasing mechanisms also typically provide an increased resistance to axial motion in the fore and aft directions during engagement and disengagement of the gears for the selected rail or shaft position.